1. Field of the Invention
The present invention relates to devices that interconnect LAN segments and/or Data Terminal Equipment (DTE) in general and, in particular, to the type of devices that use switching fabrics to make direct connections between ports in the devices.
2. Prior Art
The use of interconnecting devices, termed (Local Area Network) LAN Switch, for interconnecting LAN segments to enable communications between devices on different LAN segments and/or communication between other devices and servers connected to ports of the LAN Switch is well known in the prior art. A conventional LAN Switch or LAN Switch System includes a plurality of ports connected by dedicated port modules to a switching fabric. Devices on the ports are directly connected via the switching fabric. The attraction for LAN Switches is that they provide point-to-point communication in an environment that would otherwise provide shared media communication. The point-to-point communication is effected between two ports and, as a consequence, the overall performance and throughput of the network are increased.
One of the major problems in a LAN Switch System is determining which ports should be connected together for a given LAN frame to be transported through the LAN switch system. Since a port can be communicating with several other LAN ports over a period of time, the connection decision has to be made on a frame by frame basis and in a timely manner. In the prior art, the decision is made on the input side of the switch port. This requires that each input port knows everything about each output port and, in a multiport switch, the overhead to keep this information grows exponentially.
In order to make a fast decision regarding where to send a frame, large numbers of output port addresses are kept at each input port. The typical LAN switch uses a Contents Address Memory (CAM) and/or equivalent look-up mechanism using some external RAM to store all the output port addresses at each input port. A CAM is used in order to reduce the time needed to determine the port to which the LAN frame is to be sent. Usually an address is matched against an entry in the CAM in order to determine where to route the frame. The CAM has the characteristic of parallel comparison and can output information identifying the output port, hereafter called Port of Exit (POE), if a match occurs. The addition of a CAM at each port increases the cost of the system. In addition, the complexity of the system is also increased, since each CAM has to be updated whenever a new device is added to the network. Consequently, there is a need for a low cost, efficient and simple Routing Device for routing frames in a LAN Switch.
It is, therefore, an object of the present invention to provide a more efficient LAN Switch System than has heretofore been possible.
It is another object of the present invention to provide low-cost LAN Switch.
It is yet another object to provide a low cost, efficient and simple Routing Device for use in a LAN Switch.
The above and other objects are achieved by providing a LAN Switch with a Routing Device including input logic disposed at the input side of a port and a copy logic disposed at the output side of the port. The input logic builds a LAN Switch Header (LS Header), appends it to a frame and forwards the appended header and frame to the switch fabric. The copy logic is a simple register based compare mechanism that copies frames based upon information in the LS Header and information, termed port configuration, previously stored at the output port. If the frame is copied, it is forwarded to the port associated with the copy logic.
In particular, the input side of the Frame Processing Unit (FPU), at each one of the ports, includes a circuit arrangement or chip (termed a Quad MAC, Medium Access Control) which partitions a LAN frame into segments which are stored in N (N being a numeral) sets of 64 bytes ping pong buffers. The Round-Robin Data Movement System builds a four byte LAN Switch (LS) Header (details set forth below) which is appended to each segment of a LAN frame as it is forwarded to the switch fabric.
The output side of the FPU, at each one of the ports, includes Logic/Compare systems which monitor the LS Header on the switch fabric to decide if a sector is to be copied and forwarded to a particular port. Each port has a dedicated Logic/Compare system connected to the switch fabric and makes a copy or no-copy decision based upon the algorithm set forth below. A Copy-In Logic Circuit writes all copied segments into a Packet Memory and generates a Buffer Table with entries indicating the locations of segments in the Packet Memory. A Play-Out Logic Circuit uses the contents in the Buffer Table to move segments of data from the Packet Memory to ping pong data buffers to the Quad MACs and to dedicated ports connected to said Quad MACs.
One important feature of the present invention is that a common chip design is used at each port of the switch system. By using a common chip design, the overall cost of the switch is further reduced.
The present invention provides several benefits including the following:
The Switch System does not require a CAM device (or equivalent external memory lookup function), thus reducing system costs by allowing simple register based compare logic.
The Switch System does not require each input port to know about each output port, thus reducing costs and complexity.
The Switch System allows the output port to know many different aspects about its attached devices without causing significant system overhead.
Many different programmable options exists for configuring an output port for frame copying. These options allow the LAN Switch System to support diverse LAN devices including (Token-Ring, Ethernet, FDDI, etc.), Microprocessors, Broadcast Frame processors, Virtual LANs, RMON, etc.
Copy decision is made very quickly, therefore, reducing any frame latency through the switch.
Since each LAN frame is transferred on the LS Bus, it is easy to implement a xe2x80x9cpoint-to-multipointxe2x80x9d connection or a frame monitoring function.
The logic required to implement this copy decision process is very cost effective and easy to implement.